International Patent Application No. PCT/GB98/02292 describes a fuel fractioning system capable of separating the fuel into at least two continuous streams of fuel fractions having different octane ratings.
International Patent Application No. PCT/GB98/02754 describes an engine specifically designed to take advantage of the availability of two streams of fuel fractions having different octane ratings. In the latter engine, the intake system is designed such that the different fuel fractions reside in different regions of the engine combustion chambers. During high load operation, the higher octane fuel fraction is concentrated in the end-gas region remote from the spark plug with the aim of extending the knock tolerance of the engine and thereby allowing the compression ratio of the engine to be increased.
International Patent Application No. PCT/GB98/00614 describes another engine designed to take advantage of the availability of two streams of fuel fractions having different octane ratings in which the intake system is designed to promote stratification of the fuel fractions within the combustion chambers. In this case, it is the lower octane fuel fraction that is concentrated in regions remote from the spark plug with the aim of achieving controlled auto ignition under low and medium load operating conditions in order to minimise NOx emissions.
British Patent Application No. 9802766.7 describes an engine that combines the benefits of the above two proposals. The engine in this case has two-position swirl control valves in its intake ports and each combustion chamber has a single spark plug. The two-position swirl control valves serve to provide two stratified charge patterns of the fuel fractions in relation with the single spark plug such that in one position, for high load operation, the higher octane fuel fraction is concentrated in the periphery region of the engine combustion chamber in order to suppress knock and in the other position, for low and medium load operations, the lower octane fuel fraction is concentrated in the periphery region of the engine combustion chamber in order to promote controlled autoignition.